A spoiler is typically a panel hinged to the upper surface of a wing. Conventionally an array of such spoilers is provided for failsafe purposes. That is, each spoiler is controlled by an independent actuator so that, if one of the actuators fails, the remaining spoilers can still be deployed. The individual spoilers are closely spaced with ideally no gap between the spoilers. Generally, each spoiler is made from solid material such as metal or composite. Between the spoilers in a span-wise sense, solid rubber seals are used to prevent the leakage of airflow while the spoilers are retracted.
The primary function of the spoiler is to reduce lift of the wing, although a secondary effect of the spoiler is to slightly increase the drag of the wing. The drag increase is partially caused by the increase of frontal area due to the deployment of the spoiler.
By way of illustration, an aircraft wing shown in FIG. 1 has an upper surface 1; and a line of spoilers including a relatively large inboard spoiler 2 (oriented at right angles to the aircraft's direction of flight 4) and four relatively small outboard spoilers 3 (which are swept back relative to the aircraft's direction of flight 4).
The spoilers 2,3 are pivotally attached to the upper surface 1, and each is controlled by an independent actuator which can pivot the spoiler up into a deployed position, and down into an inoperative position in which the spoiler lies flush with the upper surface 1.
FIG. 2 shows the flow field for the aircraft wing with the conventional spoiler in its retracted position.
FIG. 3 shows the flow field associated with the aircraft wing with the conventional spoiler in its deployed position. The flow behind the spoiler is fully separated and completely turbulent. This turbulent flow generates large induced drag.
The spoilers may be deployed during landing approach and/or during landing. In such cases the drag introduced by the spoilers is not a problem. However, the spoilers may also be deployed during a cruise flight phase for purposes of load alleviation. For example, when an aircraft performs a manoeuvre such as a turn, or the aircraft wing is subject to a gust of wind, causing the lift of the aircraft wing(s) to increase, one or more of the spoilers can be deployed to minimise the increase in lift and the subsequent increase in the bending moment at the root of the wing where it meets the fuselage. However, the increase in drag induced by the deployed spoilers is not desirable when they are used for load alleviation. It is therefore desirable to reduce the drag induced by a deployed spoiler when it is deployed for the purpose of load alleviation.